KR20130052029A - Process for preparing dialkyl disulphides - Google Patents

Abstract

The present invention relates to a process for obtaining dialkyl disulfides from alkyl mercaptans and sulfur wherein the reaction intermediates present in the final disulfide are degraded at the end of the synthesis. This operation makes it possible to prevent degradation of the reaction intermediate which, over time, causes the reduction of the purity of the dialkyl disulfide.

Description

Process for producing dialkyl disulfide {PROCESS FOR PREPARING DIALKYL DISULPHIDES}

The present invention relates to the field of organic disulfides and polysulfides (hereinafter referred to as "organic sulfides") and more particularly to dialkyl disulfides, in particular dimethyl disulfide (DMDS), and in particular to methods for their preparation. .

Organic sulfides are widely used in the majority of the chemical industry and in particular in the petrochemical industry. In particular, dimethyl disulfide is used as an agent for sulfiding catalysts for hydrotreating petroleum feedstocks and as feedstock additives for steam cracking, citing only some possible uses of these compounds. will be.

Compared to other products used in such applications, for example commercial di- tert - alkyl polysulfides, organic sulfides and especially DMDS have many advantages, in particular high sulfur content (68%) and non-coking ) Decomposition products (H ₂ S, CH _{4 for} DMDS). Furthermore, in such applications, DMDS generally results in a higher level of performance than other commercial products commonly used, for example di- tert -alkyl polysulfides.

Among the known synthesis methods of organic sulfides, a particularly efficient and economical process is the oxidation with sulfur of alkyl mercaptans, for example the oxidation with sulfur of methyl mercaptan according to the following reaction in the synthesis of DMDS:

.

.

Oxidation with sulfur of the alkyl mercaptans, catalyzed by organic or inorganic, homogeneous or heterogeneous, basic agents, under batch or continuous conditions, is hydrogen sulfide and also dialkyl polysulfides (eg, synthesis of DMDS). Is accompanied by the release of dimethyl polysulfide CH ₃ S _x CH ₃ ) having a sulfur grade x of greater than 2.

In order to produce DMDS according to the process of oxidation with sulfur, which exhibits high yield and limited production of DMPS (dimethyl polysulfide having a grade of more than 2), patent EP 0 446 109 is intended to remove unwanted by-products. , A manufacturing process comprising two reaction zones interrupted by an intermediate degassing zone followed by a distillation zone is described.

While providing a good level of performance in terms of yield and selectivity to DMDS, the process has been shown to result in a final product comprising an insignificant amount of methyl hydrodisulfide (CH ₃ SSH). The amount generally varies from about 200 ppm to about 800 ppm, especially when high DMDS productivity is required.

The result of this impurity, which can be considered as a reaction intermediate, results in slow decomposition over time, giving methyl mercaptan and dimethyl trisulfide by reaction with dimethyl disulfide according to the following reaction:

.

.

Moreover, the instability of methyl hydrodisulfide (CH ₃ SSH, CAS No .: 6251-26-9) is described in H. Bohme and G. Zinner, "Justus Liebigs Annalen der Chemie" 585 , (1954), 142-9], wherein the methyl hydrodisulfide CH ₃ SSH is reacted with itself according to the following reaction Decomposition at gives dimethyl trisulfide and H ₂ S:

.

.

For the synthesis of DMDS by oxidation with sulfur, very low concentrations of CH ₃ SSH do not allow reactions between the products themselves and are more preferred with DMDS, a product mainly present in the medium.

The increase in the methyl mercaptan content in the DMDS is due to the volatile impurities in the DMDS (traces of methyl mercaptan and traces of dimethyl sulfide (DMS)) removed in a further distillation step, as described in patent application EP 0 976 726. Make the synthesis of DMDS not cost effective.

In fact, the impurities provide a very unpleasant, aggressive odor to DMDS, which is considered to cause serious problems while the user handles the product.

However, DMDS obtained by the release of volatile impurities still contains trace amounts of CH ₃ SSH. In addition, the simple removal of the impurities by distillation results in significant DMDS yield loss. This is because CH ₃ SSH has a much lower volatility than methyl mercaptan and DMS, and has a boiling point of 108 ° C., which is very close to the boiling point of DMDS (at boiling pressure, 107 ° C. to 110 ° C.). Therefore, it is very difficult to separate the products (DMDS and CH ₃ SSH).

It is therefore a primary object of the present invention to provide a process which, in the case of the synthesis of said alkyl hydrodisulfide impurities, for example DMDS, can possibly reduce or even eliminate very close to CH ₃ SSH. .

It is also an object of the present invention to remove the alkyl hydrodisulfide impurities without significant loss of dialkyl disulfide yield.

Surprisingly, it has been found that by passing through the basic catalyst of the reaction crude mainly comprising the dialkyl disulfide, the rate of decomposition of the alkyl hydrodisulfide can be significantly increased in the presence of the dialkyl disulfide.

In the remainder of this specification, the expression “reaction crudes comprising predominantly dialkyl disulfides” is intended to mean the reaction medium in which oxidation with sulfur of one or more alkyl mercaptans is carried out by basic catalysis.

Preferably, the reaction crude is a reaction crude in which hydrogen sulfide is separated (eg, by distillation, stripping, etc.), more preferably the reaction crude is separated without reacting (eg For example, distillation) is a reaction crude of the alkyl mercaptan.

Advantageously, the reaction crude is a reaction crude of hydrogen sulfide and residual alkyl mercaptans, as well as ("heavy") polysulfides, and optionally also the trace amounts of alkyl mercaptans and alkyl sulfides, eg For example, it is separated by distillation.

Accordingly, according to the first subject matter, the present invention relates to a process for the treatment of a reaction crude that contains mostly dialkyl disulfide obtained by oxidation with sulfur of one or more alkyl mercaptans in an industrial apparatus. A method of bringing an agent into contact with one or more basic catalysts is provided. The term "alkyl mercaptan" is intended to mean a compound of the formula RSH, wherein R is 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and more preferably 1 carbon atom. Linear or branched alkyl radicals of from 4 to 4. The alkyl radical R is also halogen, amino, alkylamino, dialkylamino, carboxyl, alkylcarbonyloxy, alkoxycarbonyl, hydroxyalkyl, alkoxy, mercaptoalkyl, alkylthio, alkylcarbonylamino and alkylaminocar It may be substituted with one or more groups, which may be the same or different, selected from bonyl.

Preferably, R represents a linear or branched, unsubstituted alkyl radical having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. Fully preferably, the alkyl mercaptan is methyl mercaptan.

The term "dialkyl disulfide" is intended to mean a compound of the formula RSSR, wherein R is as defined above. Fully preferably, the dialkyl disulfide is dimethyl disulfide (DMDS).

Thus, the process according to the invention is very particularly suitable for the synthesis of dimethyl disulfide, from which impurity methyl hydrodisulfide has been removed, without any loss of yield. Removal of the hydrodisulfide is carried out using one or more basic catalysts.

The basic catalyst can be of any type known to those skilled in the art. The basic catalyst is preferably heterogeneous with respect to the reaction medium in order to enable its subsequent separation. Thus, the basic catalyst is, for example, an anion exchange resin such as Amberlyst® from Rohm & Haas. A21, a basic catalyst in the form of a free amine, sodium oxide and / or potassium oxide, magnesium oxide (MgO) and the like. Preferably, the basic catalyst is an anion exchange resin.

The reaction for basic catalysis of the reaction crude is carried out in a separate step after the synthesis by oxidation with sulfur. In other words, the reaction crude is advantageously applied to one or more tablets as described later, followed by impurity alkyl hydrodisulfide RSSH (without any significant loss of yield of dialkyl disulfides, especially dimethyl disulfide). Wherein R is as defined above), in particular in a further step consisting of a basic catalysis which allows the removal of CH ₃ SSH.

The inventors have surprisingly found that in the subsequent isolated basic catalysis, the rate of decomposition of said alkyl hydrodisulfide in the presence of the corresponding dialkyl disulfide, in particular in the presence of dimethyl disulfide, will be greatly accelerated. Found that it can.

According to one preferred embodiment, the basic catalyst used to reduce the alkyl hydrodisulfide content in the reaction crude mainly comprising alkyl disulfide, to provide the reaction crude mainly comprising dialkyl disulfide, It is of the same type or even the same basic catalyst used for the oxidation reaction of sulfur with alkyl mercaptans.

According to another aspect, the invention relates to a process for the preparation of dialkyl disulfides, the process comprising at least the following steps:

a) 산화 oxidation with sulfur of the alkyl mercaptan by basic catalysis, to obtain a first reaction crude mainly containing the corresponding dialkyl disulfide;

b) stripping the formed H ₂ S;

c) 증류 distillation of the residual alkyl mercaptan;

d) separation of the heavy product (polysulfide);

e) a final topping step to allow removal of the last traces of volatile compounds;

f) the stream exiting from step a), more suitably from step b), preferably from step c), more preferably from step d), or from step e), Contacting a basic catalyst that enables removal of said alkyl hydrodisulfide by conversion of alkyl hydrodisulfide to dialkyl sulfide or dialkyl polysulfide;

g) recovering said dialkyl disulfide containing a low alkyl hydrodisulfide content.

The expression "low alkyl hydrodisulfide content" is generally intended to mean a content of less than 50 ppm by weight, preferably less than 10 ppm by weight, more preferably less than 5 ppm by weight.

The process for the synthesis of the dialkyl disulfides described above is particularly suitable for the synthesis of dialkyl disulfides of the general formula RSSR, wherein R is as defined above. The method is completely suitable for the synthesis of dimethyl disulfide.

Of the processes described above, the step a) of oxidation of the alkyl mercaptan with sulfur is carried out in a conventional manner known to the person skilled in the art. This step is described, for example, in patent application EP 0 976 726. For example, step a) is, in the case of oxidation with sulfur of methyl mercaptan, under high temperature conditions and under pressure, for example at 20 ° C. to 100 ° C., under 2 to 15 kPa, typically, for example, At about 70 ° C., it may be carried out at about 6 kPa.

Steps b), c), d) and e) are purification steps, ie to remove at least partly and ideally all of the unwanted by-products present in the reaction crude obtained at the end of step a) above. Included. More specifically, steps b), c), d) and e) respectively correspond to the removal of H ₂ S, alkyl mercaptans (starting reactants), heavy products and traces of volatile compounds.

Each of these "purification" steps b), c), d) and e) can be carried out according to any method known to those skilled in the art, such as stripping, distillation, decanting and the like.

Removing the alkyl hydrodisulfide and providing a dialkyl sulfide or a dialkyl polysulfide, in this part, corresponds to a separate chemical reaction which is subsequently carried out in the presence of a basic catalyst, which step after a), b), c), d) or e), preferably after step a), b), c) or d), preferably after step b), c) or d), Particularly preferably after step d).

As such, according to a very particularly preferred embodiment, step f) of the conversion by basic catalysis is performed immediately before the final topping step e).

For the synthesis of dimethyl disulfide, the basic catalysis step f) is advantageously carried out after the product separation step d), ie after the product distillation column 6 and the final distillation column as described in Figure 2 of patent application EP 0 976 726. 7 is performed before.

Another advantage associated with the process according to the invention is that it can increase the industrial production of dialkyl disulfides. In fact, in processes commonly used today, as described, for example, in patent application EP 0 976 726, the workers are responsible for the formation of organic hydrodisulfides which cause the unpleasant odor of the dialkyl disulfides as mentioned above. By self-degradation, minimization is looking for a way. One way to limit the formation of the hydrodisulfide is to slow the oxidation reaction with sulfur of the alkyl mercaptan by limiting the rate of introduction of the alkyl mercaptan into the oxidation reaction.

In addition to the conventional process, the process of the present invention consisting of basic catalysis of the reaction crude to enable conversion of the alkyl hydrodisulfide, increases the rate of introduction of the starting alkyl mercaptan by about 30% to 100%. It is possible to let. This makes it possible to significantly increase the overall productivity of the industrial synthesis of dialkyl disulfides.

For example, for the synthesis of dimethyl disulfide, the initial flow rate of methyl mercaptan is about 950 kg / h (in a conventional process, methyl hydrocapacity by an additional step in the basic catalysis of the reaction crude according to the invention). In the absence of basic catalysis for the conversion of disulfide).

In other words, compared to a synthesis without a “finishing process” catalytic reactor, from about 2000 kg / h / m ³ of catalyst (of sulfur main oxidation) to about 3000 kg / h / m ³ of catalyst (main sulfur using) An increase in productivity per m ^{3 of} catalyst) of the oxidation reaction was observed.

As such, according to another aspect, the present invention provides the sulfur of alkyl mercaptans of formula RSH for increasing the overall productivity of the industrial synthesis of dialkyl disulfides of formula RSSR, wherein R is as defined above. The use of at least one basic catalyst for the reaction crude of oxidation with.

The accompanying FIG. 1 shows an industrial apparatus for purifying dialkyl disulfide synthesis reaction crude (as described in patent application EP 0 976 726 for the synthesis of dimethyl disulfide or DMDS).

The degassing column 1 contributes to the complete removal of H ₂ S dissolved in the reaction crude left the reactor via pipe R through pipe 20 . Distillation column 2 makes it possible to separate most of the excess alkyl mercaptan (methyl mercaptan in the case of the synthesis of DMDS) through pipe 22 in order to reuse it in the oxidation reaction.

At the outlet of the column 2 , the mixture is conveyed through a pipe 23 to a second distillation column 3 , wherein the residual dialkyl polysulfide (dimethyl synthesis sulfide in the case of the synthesis of DMDS) may optionally be reused in the oxidation reaction. At the bottom of the column via pipe 24 .

Dialkyl disulfide (eg DMDS) collected at the top of column 3 via pipe 25 is introduced into a third distillation column 4 where the volatile impurities such as methyl mercaptan and dimethyl sulfide (synthesis of DMDS) ) Is removed at the top of the column through pipe 26 . The dialkyl disulfide (eg DMDS) is collected at the bottom of the column through pipe 27 .

FIG. 2 is a schematic similar to that shown in FIG. 1, further comprising a reactor C for basic catalysis according to the present invention. In FIG. 2 shown in a preferred embodiment of the present invention, reactor C which enables basic catalysis is located between column 3 and column 4, ie after the product separation step d) and before the final topping step e).

The invention will be illustrated by the following examples which are not intended to limit the nature of the invention as claimed in the appended claims.

In these embodiments, the passing speed on the basic catalyst for the conversion of the alkyl hydrocarbyl disulfide may be mentioned as an hourly space velocity (HSV), h ^- are shown as ^1, for the basic hourly space flow rate of the reactant It is equal to the ratio of the volume of the conversion catalyst.

Example  One According to EP 0 976 726 with better productivity conditions, without basic catalytic conversion DMDS  synthesis ( Comparative example )

a) Equipment:

Attached FIG. 1 is a schematic of the apparatus used wherein the reaction crude was due to the oxidation reaction with sulfur of methyl mercaptan (as described in patent application EP 0 976 726).

The degassing column 1 contributed to complete removal of H ₂ S dissolved in the reaction crude left the reactor via pipe R through pipe 20. Distillation column 2 made it possible to separate most of the excess of alkyl mercaptan through pipe 22 in order to reuse it in the oxidation reaction.

Column 3 made it possible to separate residual dimethyl polysulfide (DMPS) through pipe 24 for reuse in the oxidation reactor.

b) Procedure:

Methyl mercaptan (MM) was introduced into the reactor in a liquid state, under pressure, at a flow rate of 1440 kg / h. Liquid sulfur (S) was introduced into the first reactor at a flow rate of 240 μg / h (MM / S molar ratio = 4).

The oxidation reactor (reaction volume 300 ml) was prepared with 20 g of dry Amberlyst ^? A21 resin was contained. The operating pressure was maintained at 5.5 bar (relative) and the temperature at 40 ° C. Thereafter, the first reactor was transferred to a degasser to treat the reaction mixture leaving.

After treatment, H ₂ S dry Amberlyst of the glass mixture 94 ^g? The reactor was transferred to a second reactor filled with A21 resin. The operating pressure was maintained at 5.5 bar (relative) and the temperature at 50 ° C. The mixture leaving the reactor was then introduced into a degasser for the removal of H ₂ S.

The mixture leaving degassing column 1 was introduced into first distillation column 2 through pipe 21 to remove virtually all excess methyl mercaptan. The methyl mercaptan could be reused as the reactant was introduced in an oxidation reaction through pipe 22. The mixture leaving the column 2 was transferred to a second distillation column 3 via pipe 23 where the DMPS was removed at the bottom of the column via pipe 24 optionally for reuse in the oxidation reaction.

DMDS collected at the top of column 3 through pipe 25 was introduced into a third distillation column 4 where volatile impurities such as methyl mercaptan and dimethyl sulfide were removed at the top of the column through pipe 26. The DMDS collected at the bottom of the column through pipe 27 had a composition of the following weight (all values are expressed by weight):

DMDS: 99.9%

DMTS: 334ppm

CH ₃ SSH: 377 ppm

MM: 32ppm

DMS: <2 ppm (detection limit)

The test indicated that CH ₃ SSH was present in the final product when the synthesis of DMDS was performed under conditions of better productivity than patent application EP 0 976 726 (higher reactant flow rate and oxidation reactor temperature).

Example  2:  Synthesis according to the invention

Example 1 DMDS crude was taken containing 377 ppm by weight of CH ₃ SSH. The 337 ppm could be returned to 226 ppm of CH ₃ SH in the final product over time.

The DMDS was prewashed with methanol and Amberlyst ^? To a bed of A21 basic resin (Rohm & Haas) and to remove the water contained in the resin (5 g of dry resin, ie 14.3 ml) at a rate of 180 g / h (171 ml / h, HSV of 12 h ^{- 1} ), and dried at a temperature of 40 ° C for 2 hours. The CH ₃ SSH was no longer detected by gas chromatography (detection limit about 2 ppm by weight) in the discharge of the tubular reactor containing the resin.

Example  3:

At this point another DMDS crude was taken containing 428 ppm of CH ₃ SSH (the 428 ppm could be returned to 257 ppm of CH ₃ SH in the final product over time).

The DMDS was pre-dried (5 g, ie 14.3 ml) at a rate of 530 g / h (505 ml / h, ie 35 h ^{- 1} HSV), for 2 hours at a temperature of 40 ° C., Amberlyst ^? It was transferred to a bed of A21 basic resin (Rohm & Haas). The CH ₃ SSH was no longer detected by gas chromatography (detection limit about 2 ppm by weight) in the discharge of the tubular reactor containing the resin.

Example  4:

A DMDS crude containing 219 ppm of CH ₃ SSH (the 219 ppm could be returned to 131 ppm of CH ₃ SH in the final product over time) was taken.

The DMDS was added at a rate of 1000 g / h (952 ml / h, ie HSV of 67 h ^{- 1} ) for 2 hours and then at a rate of 2000 g / h (1904 ml / h, ie 133 h ^{- 1)} . ), Pre-dried for 2 hours at a temperature of 40 ° C. (5 g, ie 14.3 ml), Amberlyst ^? It was transferred to a bed of A21 basic resin (Rohm & Haas).

At the two flow rates, the CH ₃ SSH was no longer detected by gas chromatography at the discharge of the tubular reactor containing the resin (about 2 ppm by weight detection limit).

Example  5:

A DMDS crude containing 239 ppm of CH ₃ SSH (where 239 ppm could be returned to 140 ppm of CH ₃ SH in the final product over time) was taken.

The DMDS was pre-dried at a rate of 2000 g / h (1904 ml / h, ie HS133 of 133 h ^{- 1} ) for 2 hours at a temperature of 20 ° C. (5 g, ie 14.3 ml), Amberlyst ^? It was transferred to a bed of A21 basic resin (Rohm & Haas).

The CH ₃ SSH was no longer detected by gas chromatography (detection limit about 2 ppm by weight) in the discharge of the tubular reactor containing the resin.

The DMDS used in this example, which initially contained 441 ppm of dimethyl trisulfide (DMTS), contained 809 ppm after passage on the resin, ie in an increase of 368 ppm. The value of 368 ppm was very close to the theoretical maximum of 376 ppm (which is obtained when each mole of CH ₃ SSH is considered to provide 1 mole of DMTS).

Claims (10)

In an industrial apparatus, a process for the treatment of a reaction crude that mostly contains dialkyl disulfides obtained by oxidation of one or more alkyl mercaptans with sulfur, wherein the reaction crude is contacted with one or more basic catalysts. The compound of claim 1, wherein the alkyl mercaptan is a compound of formula RSH, wherein the dialkyl disulfide is a compound of formula RSSR, wherein R is 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably A linear or branched alkyl radical having 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, wherein said alkyl radical R is also halogen, amino, alkylamino, dialkylamino, carboxyl, alkylcarbonyloxy, alkoxycar And is capable of being substituted with one or more groups, which may be the same or different, selected from carbonyl, hydroxyalkyl, alkoxy, mercaptoalkyl, alkylthio, alkylcarbonylamino and alkylaminocarbonyl. The compound of claim 1 or 2, wherein the alkyl mercaptan is a compound of formula RSH, and the dialkyl disulfide is a compound of formula RSSR, wherein R is 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, More preferably a linear or branched, unsubstituted alkyl radical having 1 to 4 carbon atoms. The method of claim 1, wherein the alkyl mercaptan is methyl mercaptan and the dialkyl disulfide is dimethyl disulfide. 5. The process according to claim 1, wherein the basic catalyst is a heterogeneous catalyst with respect to the reaction medium. 6. 6. The basic catalyst according to any one of claims 1 to 5, wherein the basic catalyst is selected from anionic exchange resins, basic catalysts in the form of free amines, alumina doped with sodium oxide and / or potassium oxide, magnesium oxide (MgO) and the like. Preferably, the basic catalyst is an anion exchange resin. A process for preparing a dialkyl disulfide, comprising at least the following steps:
a) oxidation with an alkyl mercaptan with sulfur by basic catalysis to obtain a first reaction crude mainly containing the dialkyl disulfide;
b) stripping the formed H ₂ S;
c) distillation of said residual alkyl mercaptan;
d) separation of the heavy product (polysulfide);
e) a final topping step to enable removal of the last traces of volatile compounds;
f) withdrawing the stream exiting in step a), more suitably in step b), preferably in step c), more preferably in step d) or in step e); Contacting a basic catalyst that enables removal of said alkyl hydrodisulfide by conversion of alkyl hydrodisulfide to dialkyl sulfide or dialkyl polysulfide;
g) recovering said dialkyl disulfide containing alkyl hydrodisulfide in an amount of less than 50 ppm by weight, preferably less than 10 ppm by weight, more preferably less than 5 ppm by weight. 8. The method of claim 7, wherein said alkyl mercaptan is methyl mercaptan and said dialkyl disulfide is dimethyl disulfide. The process according to claim 7 or 8, wherein step f) for removing said alkyl hydrodisulfide and providing a dialkyl sulfide or a dialkyl polysulfide in the presence of a basic catalyst comprises steps a), b), after c), d) or e), preferably after step a), b), c) or d), preferably after step b), c) or d), particularly preferably step d The method can be performed after). One for reaction crudes containing mostly dialkyl disulfides of formula RSSR, obtained by oxidation with sulfur of alkyl mercaptans of formula RSH, in order to increase the overall productivity in the industrial synthesis of the dialkyl disulfides. For the use of the above basic catalysts, R represents a linear or branched alkyl radical having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms. , The alkyl radical R is also halogen, amino, alkylamino, dialkylamino, carboxyl, alkylcarbonyloxy, alkoxycarbonyl, hydroxyalkyl, alkoxy, mercaptoalkyl, alkylthio, alkylcarbonylamino and alkylamino Use that can be substituted with one or more groups, which can be the same or different, selected from carbonyl.

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